The problem of cleaning water from impurities, especially from oil spills, appears one of the most important problems encountered by people.
Scientists of the Moscow State University have discovered that about 25 million tons of oil get into the bio-sphere in Russia alone. It should be noted that regular oil production and delivery activities cause even more pollutions in the ocean than technological/ecological failures. Some specialists believe that up to 20% of the area of world's oceans is covered by oil films with a thickness of about tens of microns. This film hampers feeding and breathing of fish and sea animals (http://www.infox.ru/science/planet/2010/05/12/Vosstanovlyeniye_Mye.phtml).
Though oil bio-degrades in the nature, such process may last for many years. Participants of biocenosis (biotic assemblage) are capable of utilizing practically any organic compound: from methane to heavy oil fractions, but with different rates. Micro-organisms oxidize toxic compounds, converting them into non-dangerous substances. Heavy fractions sedimentate on the bottom (seabed), wherein they are ‘buried’ in the soil by bottom dwellers.
Another aspect of the problem of oil water pollution relates to the fact that an oil film having a thickness of only one molecule (10-20 nanometers) reduces evaporation from the water surface by about 20%. An oil film having a thickness of 50 micrometers reduces evaporation from the water surface by about 60%. Such film also diminishes the vertical natural intermingling of water. It is understood that such an accumulated solar energy reservoir is capable of significant influence as to regional weather, for instance it can feed hurricanes with energy.
There are presently a lot of methods developed for cleaning water from oil. These methods can fall into a number of large groups.
1. Mechanical cleaning methods. A wide-spread mechanical cleaning method essentially comprises an extraction of oil by means of gravity sedimentation with a subsequent recapture thereof by special devices called oil-gasoline traps, thickening devices, or even hand separation devices. The mechanical machines however are not efficient for cleaning water from oil nano- or micro-particles.
Another kind of mechanical methods is filtration of water. Filters are efficient in cleaning water from micro-particles of oil. A major disadvantage of filters is fast accumulation of oil therein that leads to decreasing the cleaning efficiency and device productivity. Newly proposed nano-sorption filters also quickly accumulate micro-particles of oil and require often replacement.
Nowadays, the most promising mechanical methods for cleaning water from oil nano- and micro-particles are membrane purification methods. In these methods, semipermeable membranes are used. A semipermeable membrane is a partition capable of passing water therethrough, while entrapping particles having a diameter greater than the water molecule's diameter. Such membranes consist of cells with a diameter sized from tens of nanometers (made of materials: polycarbonate, polyether) to hundreds of nanometers (made of materials: cellulose ester, polytetrafluorethylene, polyethylene, polypropylene). A semipermeable membrane requires water supply with a pressure from tens to hundreds of atmosphere. A major drawback of the membrane purification methods is still fast accumulation of oil particles in the membrane.
2. Chemical cleaning methods. They can also be employed for cleaning water from nano- and micro-particles of oil. Many chemical cleaning methods contemplate adding certain chemical reagents into water, wherein the chemical reagents are capable of reacting with oil and sedimentating oil particles in the form of insoluble precipitations. These chemical cleaning methods usually allow for a reduction of oil pollutions by 95%. However, the use of the chemical reagents for a further increase of cleaning quality leads to an intensification of water pollution by the chemical reagents, therefore the purification capacity of these chemical cleaning methods is limited.
Another kind of chemical cleaning methods envisages adsorbing the oil particles by various types of adsorbents, for instance, aluminosilicate micro-spheres or aluminum oxide, with a subsequent burning-off of the oil particles from the sorbent pores. The cleaning extent of this method can reach up to 98%, but it's limited by the area of oil pollution. In the other words, the method can be employed for cleaning oil polluted water located in limited and substantially immovable boundaries. It is difficult to utilize the method in fast flowing rivers and waved seas. Besides, the method still cannot be used for full purification of water.
3. Biological methods of water cleaning are based on the use of special micro-organisms (bacteria) fed by oil and thereby destroying the oil particles. At present, there are known more than one thousand of micro-organisms capable of such processing hydrocarbons of different classes. Bacteria life activity products and dying bacteria themselves can be easily digested by aboriginal micro-flora contained in the water reservoir, forming bottom silt. The method allows attaining an oxidation efficiency of oil hydrocarbons up to 99%.
However, the aforementioned biological cleaning method can be efficiently used for cleaning oil nano- and micro-particles located in a water area with limited and substantially immovable boundaries. It is difficult to utilize the method in fast flowing rivers and waved seas. Besides, for full purification of water, a very large quantity of micro-organisms is required. As the concentration of oil in water reduces, the amount of food for the micro-organisms decreases that causes death of the micro-organisms. This leads to the necessity of feeding the micro-organisms using special food, and this food also pollutes the water.
For a long time, the instant inventors were involved in a process of burning out of water-contained masut (boiler oil) and other petroleum-derived products and designing various dispersers therefor. The dispersers contained a water-masut mixture that was moving under cavitation (Russian Federation Patents: RU2306972, RU2310132, RU2310133). As known, during cavitation, a collapse of air/steam bubbles takes place with an increase of temperature (up to several thousand degrees) and an increase of pressure (up to several thousand atmospheres). This fact has led the inventors to an idea of deploying cavitation for cleaning water from nano- and micro-oil particles by means of burning-off the particles in a water flow under cavitation.
There is known a device for cleaning wastewater containing oil products described in a Russian Federation Patent RU2408540, issued 10 Jan. 2011. The device includes hydro-cyclones, cylindrical chambers mounted the hydro-cyclones' drains, sinker divided by vertical partitions into sections with perforated distribution units located therein, while the lower portion of the sinker contains a tube-like holed collector being part of a system for deposit deduction and another system of washing the deposits out, which washing system is located above the collector and symmetrically on two sides thereof and comprises supercharging tube-like telescopic collectors. The device has a shortcoming of low efficiency for cleaning water from nano- and micro-oil particles. The oil particles are extremely difficult to separate from water due to the fact that their densities are almost equal and the adhesion forces of the oil and water particles are significantly great.
Another related art device for cleaning and deactivating a water medium is described in a Russian Federation Patent RU2170713, issued 20 Jul. 2001. The device comprises a circulation contour including a jet pump with an ejector and a cavitation chamber, photo-chemical reactor and a filter. This device is used for cleaning and deactivation (de-contamination) of water from organic, non-organic, toxic pollutions, and from pathogenic micro-flora. The cavitation process is provided by means of an ultra-sound emitter. It can also comprise an additional cleaning means in the form of at least one UV-radiator. The device has a disadvantage of low efficiency for cleaning water from oil nano- and micro-particles. It consumes two—three times more energy than the claimed device does.
The closest related art device (herein also called a ‘prototype’) for cleaning water from oil nano- and micro-particles, known to the instant inventors, is described in a Russian Federation Patent 2343951 issued 20 Jan. 2009. The prototype includes a unit for dynamic processing water polluted by oil (herein further called a ‘dynamic water processing unit’), which unit comprises a housing with a channel for water flow, wherein the channel has a section (portion) characterized with a variable passage cross-section gradually decreasing along the water flow direction.
Besides, the housing contains a divisional container with a horizontal partition that divides the container into an intake and a gravitation compartments. Additionally, the container has a number of vertical partitions, some of them are made holed. The device also comprises a branch pipe (outlet pipe fitting) for outlet of gases in the upper portion of the divisional container, and another branch pipe for outlet of water and oil. The prototype device purifies water by means of coagulation, chemical processing, adsorption, and rotation in a centrifuge.
The prototype has a shortcoming of low efficiency of cleaning water from oil. The prototype device can hardly separate the oil particles, including nano- and micro-particles, from water due to the fact that their densities are almost equal, and the attraction forces therebetween are extremely intense. It should be noted that the prototype does not use cavitation for cleaning water from oil particles that the instant inventors also consider a shortcoming.
The claimed device has a design in a way similar to a design of a disperser used for preparation of fuel mixtures. Hence, some terms form a publication http://newtechnolog.narod.ru/articles/34article.html were used in this description.
A number of dispersers have been described in the related art, for example: a book by Ganiev R. F. et al “Wave technology for preparation of alternative fuels and efficiency of combustion thereof” published by Scientific Publishing Center “Regular and Chaotic Dynamics” (Moscow 2008), page 116; Russian Federation Patents: RU2293599, RU2336938, RU2285558. The latter describes a channel for moving a fuel mixture and units providing cavitation during a streamline flow of the mixture around thereof. RU2239491, (issued 10 Nov. 2004) teaches a disperser comprising a housing with a channel for a liquid fuel, which channel includes a section with a variable passage cross-section decreasing along the channel's length, a minimal passage cross-section, and a section with a variable passage cross-section increasing along the channel's length.
The aforementioned related art dispersers were experimentally used (researched) by the instant inventors for cleaning water from oil. The experiments revealed the following disadvantages of these dispersers:                The initiation of cavitation requires a high speed of liquid flow. For a liquid flow moving along the channel, in case of non-disturbance conditions, the experiments showed that the cavitation process launched at a significantly greater flow speed than a flow speed observed for a liquid flow moving along the channel in case of disturbance conditions. A reduction of the speed corresponding to the launch of cavitation was achieved by providing transverse corrugations, or protrusions and deepenings, formed on the channel's surface that were located on the section with the decreasing passage cross-section, as taught in RU2293599. RU2336938, teaches that the speed, corresponding to the launch of cavitation, can be reduced by placing a plate at the entrance of disperser that closes a portion of the channel's passage cross-section.        Cavitation occupies a relatively small volume inside the channel.        
The aforesaid disadvantages are overcome in the instant invention.